Method of electroforming gun barrels and liners



April 28, 1953 A. BRENNER 2,636,349

METHOD OF ELECTROF'ORMING GUN BARREL-S AND LINERS Filed Dec. 13, 1946Patented Apr. 28, 1953 UNITED STATES ATENT OFFICE METHOD OFIELECTROFORMENG GUN BARRELS ANU LINERS Abner Brenner, Ghevy Chase, Mela,assignor to the United States of rimerica as represented by theSecretary of. War.-

d Claims.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes. without the payment. of anyroyalty thereon.

' My invention. relates to. methods of making. gun barrels, barrelliners and the like; and it has particular reference to techniques -formanufacturing rifled gun barrels and liners from certain relativelyhardmetals.

Broadly stated, a. principal. object. of my inv'ention is to provide a.method for making rifledbore. gun barrels and liners out of metals, suchas, cobalt, tungsten, molybdenum and alloys thereci, winch are. toohard. to machine or cast by the usual. commercial processes.

A more specific object: of my invention is to provide a method, formaking rifled gun bores without having to storm. the ri-fiings byconventional machining, swaging or breaching operations.

' Another object isto simplify the manufacture. of. gun barrels andliners whose walls have variously designed tapers and whose bores haveconiplexrifiings.

A further object is. to reduce the time and effort needed to. make suchgunv barrels and liners.

A still. further object is to improve the economy of gun manufacture.

The exact manner in which I accomplish these objects will become evidentas this disclosure proceeds. Briefly stated, however, the process.consists of electrol'orming. gun barrels or liners by plating a.suital'ole metal. or alloy upon a master. This master is. aprecision-made negative of the lands and grooves comprising the desiredbore. rifiings of a gun barrel or liner.

" The plating upon the master carried on until a sheath-tn positive is.built up therearound to a suitable thickness. This positive, which isactually an electroiormed gun barrel or barrel-liner consists, oi a tubewhose bore faithfully reproduces the lands. and grooves of the negativeor master. When completely formed. the newly formed. barrel or liner isthen removed from the master and machined on its outer surface. to itsrequired outside diameter. The master is used over and over again inrepeating the process just outlined.

A preferred form of the master used in practicing my invention and theproduct which can obtained thereby may be seen by reference to thedrawings: wherein:

1 illustrates in longitudinal section a typical master or steel negativeof the required rifled gun bore, upon which a gun barrel comsec. 266) 2prised of two different metallic layers has been electrotormed, togetherwith various fittings used in the plating process;

. Fig. 2- is a cross sectional view taken from line 2'2. of the Fig. lrifled master without showing, the electroplated metal coatings includedin the Fig. 1 illustration;

3 shows the Fig. 2 master after it has been. electroplated first with athin layer of cop per, then a thicker layer of lead. and finally a flashcoating of copper;

Fig. 4 depicts the. result of electroplating a layer of hardenablegun-metal. upon the previously copper and lead plated master shown in.Fig. 3;.

Fig. 5 repeats the View of. Fig. l except that the exterior of thehardenable. gun-metal layer has been ground to provide a smooth surfacewhich is necessary in cases where a gun barrel liner is being. made. Thethus ground,v plated master is also a prerequisite in cases where a.complete gun barrel is produced by this invention as, will be evidentfrom the next drawing;

Fig. 6 shows the Fig. 5 product upon whose hardenable metal layer has.been electroplated a layer of softer and less. expensive metal to. iorma complete, rifled gun barrel;

Fig. l shows the complete electroiormed gun barrel of Fig; 6 from whosebore the master has been extracted; and

Fig. 3 shows a master similar to that of Fig. 2, etc, but made of metalother than steel, the external surface thereof being coated. with anelectroplated layer of lead.

The art of gun barrel. and gun. liner manufac ture has undergonesuccessive improvements designed to speed up and reduce the costs oftheir manufacture. Thus, for example, delicate machining of gun boreriflings ilands and grooves) has given way to swaging or broaehingoperations in making the barrels of many small arms weapons andbarrel-liners for larger caliber guns. At the same. time, theconcomitant metallurgical improvcrnents which have been made for thepurpose oi" increasing the resistance of the gun barrels or liners toerosion and corrosion, have likewise increased the hardness. of the gunmetals to the point where machining or breaching, operations are nolonger feasible. In fact, these metals are so hard that they are not.capable of being put to practical use by employing conven tional.casting methods.

Thus, the problem has been to develop a method whereby gun barrels andliners can be ecohomically and satisfactorily mass-produced from thevery hard, corrosion and erosion resisting metals now known to be mostuseful in gun manufacture. Examples of such metals are cobalt, tungsten,chromium, molybdenum and various alloyed combinations thereof.

[is earlier mentioned, I have invented a method whereby rifled gunbarrels and liners can be made from the aforementioned hard orhardenable metals without resorting to any difdcult machining, broachingor casting operations. This method is fast, very economical and capableof producing barrels and liners with excellent gun bore rifiings (suchas are represented by I4 in Fig. 7), as the following description of mymethod will make clear.

To begin with, I make a master II or negative mold of the bore of thesun which is to be manufactured. This master II may take the form of acylinder or rod whose outer wall is shaped exactly like the interiorbore of the gun being made, thus forming an exact negative counterparthaving negative riflings to (see Figs. 1-2) of the desired guns borerii'iings I 4 (see Fig. 7).

In making master II, I preferably utilize a steel rod, machining thenecessary negative rifiings I5 (see Figs. 1-2) on the rods outer wall.However, other methods and metals may be used. For example, the mastercan be made by casting a low melting alloy, such as babbit metal, into amold. Still another technique is to cast or plate a soft metal such aslead or babbit metal around a steel rod, and then provide the necessarynegative lands and grooves thereon by drawing the thus coated rodthrough an appropriate die. Regardless which method is used for makingthis master, and notwithstanding the complexity of the required gunbores rifiings and wall taper, the job of making one such master byexternal machining, etc., is obviously much simpler than the job ofmaking numerous gun barrels or liners whose bores require individualinternal machining or other operations.

Having thus obtained the master I I (see Figs. 1 to 7), the actualprocess of electroforming rifled gun barrels or layers is now capable ofbeing carried out. The first step is to attach an extractor I! (seeFig. 1) to the master. This attachment may be made by threadedconnection (not shown) or by any other convenient means. In fact, it ispossible and may even be preferable to make the extractor a continuousunit of the s master.

The next step is to carefully polish the master to remove burrs or othersurface imperfections. This is important because those imperfectionswould cause nodules in the gun barrel or liner that is subsequentlyplated upon the master, or even prevent the masters easy removal fromthe resultant electroformed product.

The master is then prepared for the electroforming operations to followby attaching at its free end (i. e., not the end to which the extractorI1 is attached) a plastic cap 26 (see Fig. 1). This cap 26 may bedesigned so that it can be pressfitted onto the master and act as amask" to prevent metallic electrodeposition beyond a certain desiredarea on the master. Obviously, however, any other means of attachingthis plastic cap or in fact any other conventional type of maskingdevice may be used for this purpose.

On the other end of the master, namely, that to which the extractor I1is connected, another masking device such as the plastic cap 21 shown inFig. 1 should be attached. One convenient way of installing cap 21 is toslidably remove the handle bar 28 from the opening 29 which extends Liltransversely through extractor I1, slip the plastic cap over theextractor into the illustrated snug fitting or press-fitted relationshiptherewith, after which the handle 28 may be returned to the position inthe extractor which Fig. 1 shows.

The master to be electroplated having thus been properly protected sothat the actual plating operations will produce the rifled barrel orliner of desired dimensions, and also so that the extractor I! will notbecome plated with the metallic coatings, the actual electroformingsteps can be begun.

When the master II is made of steel, a preferable procedure is then toapply thereon a copper coating 23 about 0.0005 inch thick (see Figs.3-4-56), from a cyanide bath. Note: Use of such a copper coating, whileoptional, is desirable as an added precaution against corrosion. Whetheror not this copper coating is applied, the next step is to electroplatean approximately 0.0003 inch coating of lead 24 (see Figs. 1-3-45-6) orother low melting point metal. If a non-corrosive metal such asstainless steel or non-ferrous metal is used for the master there is noneed for a first coating 23 of copper and, instead, the lead coating 24is applied directly thereon as shown in Fig. 8.

As will later become apparent, the product being electroformed by myprocess is removable without damage from the master because this leadenvelope 24 (which coats the master I I Figs. 34-5-6) can be melted at atemperature considerably lower than that which would have any effeet onthe master or the product electroformed therearound. The reason forusing lead, in addition to its having a relatively low melting point, isthat lead does not readily diffuse into the steel or copper of themaster. If this should happen, it would prevent the electroformedproduct (barrel I3) from being slipped off the master.

Other metals, for example cadmium, could be used in place of lead. Caremust be taken, however, to employ a metal which will not alloy (as doestin) with the metals it comes into contact with, as this would cause abond between master I I and the electroformed product that would maketheir later separation difficult.

At this point, the lead coated master II is polished by any desiredmeans to provide a smooth, bright surface. A preferred technique iselectropolishing, and a suitable material for use in that process is amixture of acetic anhydride and perchloric acid. After polishing theleaded surface, a flash or thin coating 25 of copper from a cyanide bathmay be utilized to assure that the outside wall surface of the master IIis perfectly clear and smooth preparatory to plating the desired gunbarrel or liner thereon. At this stage, the master II appears asillustrated in Figs. 3-4-5-6.

The thus polished master II, optionally provided with a copper coating25, is then placed in an electrolytic bath containing in solution thesalts of the metals from which the gun barrels or liners are to beelectroformed. The choice of metals from which to make the gun barrelsor liners may vary depending on the requirements of the user. Examples,as earlier mentioned, of the more desirable hardenable metals which maybe used include cobalt, cobalt-tungsten alloy, cobalt-molybdenum alloy,etc. The temperature of the electrolytic bath should always be somewhatbelow the melting point asses-4e The entire. gun: barrel: or." liner;may then; be:

plated with the; chosen metal about the master ll untilv the necessarywall thickness: of the finished product is attained. Or, preferred, theplating, with the special hardenable metal may be stopped after a wallthickness is attained (such as that of the layer represented. by 28 inFigs, -i--5-6-7 which is suliicicnt to house the lands and grooves of.the final. productis bore. (This particular thickness will, of course,vary with the riiiing requirements. of the individual weapon part beingmade; eg., it would be about 9.0; inch in the military type caliber .50gun.) The master, with its partially formed barrel or liner platedtherearouncl, may then be trans-- ferred to another bath containing acheaper, more abundant metal, such. as iron, and the plating processresumed until. the barrel or liner acquires a further layer such as isrepresented. by M in Figs- 6-7, and the barrel is thus built to itsrequired total cross-sectional diameter.

In making gun barrels or liners of such composite electroplatedcoatings, caution must. be observedin the selection of metals. becauseof a. possibility that cracking will occur when the product is laterannealed, due to the differences in the various coefiici'ents orexpansion- For example, I have found that a layer of nickel, plated froma strong nickel chloride bath, could.

not be used over a cobalt or a cobalt-tungsten.

all-oy'fo'r this reason. On the other hand, I have found that a goodcombination for such com-- posits coatings consists of a cobaltdungsteninner lining with the balance of. the electroformed product made up ofeither cobalt or iron.

as an extra added precaution in. a strain-free final product, it hasbeen found prelerable to grind the outside wall surface of the barrelorliner'being' electrof'ormed after a coating several hundredths of aninch thick been de-' posited on the master H (compare unground productof Fig. l with ground product shown in Fig. 5). This procedure ishelpful because the metal which plates on the master has a tendency toform a pattern duplicating the masters lands and grooves (see- Fig. i).Were the contours of those lands and grooves permitted to be thus"transmittcd throughout. the entire electroformed product, lines ofweaknes between the lands and grooves would result; Grinding toeliminate the contours or pattern of the rifiings (see Fig. 5) preventsthis occurrence.

When the: electroformed sheath or envelope (barrel. It in the drawings)has been plated to a. suificient thickness to meet the requirements ofthe desired gun barrel or barrel liner (as in Fig. 6), master H isremoved therefrom (resulting in the product shown by Fig. 7). This. isdone by heating the assembly to about 401') C. to melt and eliminate thelead coating it, the master M then being easily extracted from theelectroformed barrel [3 with the aid of the earlier described extractorIL Preferably}. prior to so heating the assembly, the handle 28 shouldbe slidably removed from extractor ii, and plastic cap 21 should beslipped oif the assembly. The other plastic cap 26 should likewise beremoved, the purpose being to avoid the possibility of high temperaturesdamaging these masking aids. Of course, if the plastic or other masksused have a sufficiently high melting point they need not be removedprior to this heating step.

A further caution, which experience has shown to be valuable inpracticing my invention, should be observed in the: actual. proness. ofextracting the master. In this extraction, the. end. of theelectroformed. barrel; I31 that bears against the extractor l1 should.be: perpendicular to the axis of that barrel [3; otherwise the hotmaster llmaybe bent. during. its extraction.

After the electroformed' barrel [3 has been. freed from. master H, itmay be heat treated to anneal. the alloy from which. the: barrel 13; was

made... The last. step in my novel. process: is: to

machine. or grindv this electroiormed barrel. It to: itsv final form in.accordance. with. the: various requirements. for its overall diametraldimensions: (which variance depends, among. other things, on whethertheproduct is to. be used as a gun barrel or a. separate reliner to beinserted into a barrel). This. machining: or grinding step can. be done.with standard. macl'iin'ery and, for purposes of: mass production, canbe readily processed with conventional cienterless. grinders.

The time-required for my entire. unique process as above described will.of course vary with the thickness. of: the l ner. or barrel desired tobe thus electrofbrmed, and. the. metals. from which those. products. areto be: made. For example, the time required to plate a 0.02 inch thickcoating, of cobalt tungsten alloy (like the metal layer 20 shown inFigs, l-4-5-6-7) for use as a gun liner inv one typical instance wasfound to be about. at hours when. av currentdensity of 2. aniperes: persquare decimeter was used. The. remainder' of the electroformed linerenvelope (similar to the metal layer 2-! shown. in. Figs; 1-6- 7) wasmade of cobalt which. was plated. on top. of the: cobalt-tungsten. alloyat: a. minimum rate or 0.005 inch per. hour.

In this specific example, an. entire liner inch.

thick, plus a. margin. for machining the outside wall surface, wasplated in. approximately three days. However, the actual time per unitproduct required of an operator during this operation was very lowbecause a large number of liners were accommodated. in. the singleplating bath, and they required no attention during the plating process.

It should be understood that the: composition of the. various alloysmentioned. above is not critical in the practice of. the. presentinvention. That is to say, practically any alloy of cobalt. and tungstenor cobalt and molybdenum may be utilized in the. process hereinabovedescribed, the sole determining criterion. being the particu-- larproperties in the finished liner or barrel which is desired by those whopractice my in- I vention. However, for the purposes of illustration,suitable alloys now will be described by reference to one manner inwhich they may be made. These alloys, and more particularly a method andbath for electrodepositing them, are disclosed in co-pending patentapplications of which I am a co-applicant.

In co-pending application Serial No. 708,566 which. I. filedon November8,. i946, jointly with Polly Burkhead and Clara A. Sentel for Method ofand Bath for Electrodepositing Tungsten Alloys, there is described abath which consists of '70 grams per liter sodium tungstate, 28 gramsper liter cobalt chloride, 100 grams per liter Rochelle salt, 50 gramsper liter ammonium chloride, and the remainder is made up of water plussufficient ammonium hydroxide required to adjust the alkalinity of thebath. This bath is operated at a temperature of about C., at a currentdensity of 1 to 3 amperes per square decimeter, and the pH is maintainedbetween 8 and 9.

In co-pending application Serial No. 708,565

which I filed on November 8, 1946, jointly with Polly S. Burkhead forCarbonate Electrolytic Bath and Methods for Electrodepositing Cobalt orCobalt-Molybdenum Alloys Therefrom, there is described a bath whichconsists of 1000 grams per liter of potassium carbonate, 15 grams perliter of cobalt chloride or cobalt sulphate, 100 grams per liter ofsodium molybdate, and the remainder is made up of water. This bath isoperated at a, temperature of between 90 and 135 C., at a currentdensity of 1 to 5 amperes per square decimeter and a pH of 11.

All the aforementioned objects of my invention have been attained bymeans of the methods and alternative techniques earlier outlined.However, it will be obvious to anyone generally skilled in the art thatmy invention can be practiced in numerous other ways without departingfrom the spirit or scope of my discoveries.

My invention is therefore extensive in its adaptation and is not to berestricted to the specific form here shown by way of illustration.

I claim:

4 l. The method of manufacturing a gun barrel having a rifled bore outof metals that are highly resistant to erosion and corrosion but are toohard to machine or cast conveniently, which COlllprises making a steelnegative form whose external dimensions substantially correspond torequired internal dimensions for the desired gun barrels rifled bore,polishing said negative form to a smooth finish, plating a thin layer oflead upon the outer surface of said negative form, thereafterelectropolishing the lead-coated negative form to a bright and smoothfinish, thereafter electroplating the metal from which said gun barrelis to be made to a desired part of the desired total thickness upon theouter surface of said lead-coated negative form at a temperature belowthe melting point of said lead coating, thereafter grinding smooth theouter surface of the metal which has been thus electroplated upon thelead-coated negative form in order to eliminate the contour of theunderlying lands and grooves from the subsequent plating, thereafterresuming electroplating the metal from which said gun barrel is to bemade as aforesaid until the desired total gun barrel thick ness plus amargin for final machining has been reached, thereafter heating the thuselectroplated negative form to a temperature high enough to melt andeliminate said lead coating from said negative form, thereafterextracting said negative form from the resultant gun barrel that hasbeen electroformed therearound, and then grinding the outside Wallsurface of the resultant gun barrel to the desired overallcrosssectional dimensions.

2. The method of manufacturing a gun barrel having a rifled bore out ofmetals that are highly resistant to erosion and corrosion but are toohard to machine or cast conveniently, which comprises making a metallicnegative form whose external dimensions substantially correspond torequired internal dimensions for the desired gun barrels rifled bore,polishing said negative form to a smooth finish, plating upon the outersurface of said negative form a thin layer of a fusible metal which doesnot readily alloy with the metal of the negative form, thereafterelectropolishing the fusible metalcoated negative form to a bright andsmooth finish, thereafter electroplating the metal from which said gunbarrel is to be made to a desired part of the desired total thicknessupon the outer surface of said fusible metal-coated negative form at atemperature below the melting point of said fusible metal coating,thereafter machining smooth the outer surface of the metal which hasbeen thus electroplated upon the fusible metal-coated negative form inorder to eliminate the contour of the underlying lands and grooves fromthe subsequent plating, thereafter resuming electroplating the metalfrom which said gun barrel is to be made as aforesaid until the desiredtotal gun barrel thickness plus a margin for final machining has beenreached, thereafter heating the thus electroplated negative form to atemperature high enough to' melt and eliminate said fusible metalcoating from said negative form, thereafter extracting said negativeform from the resultant gun barrel that has been electroformedtherearound, and then machining the outside wall surface of theresultant gun barrel to the desired overall cross-sectional dimensions.

3. The method of claim 2 in which the electroplated metal from which thegun barrel is to be made is selected from the group consisting ofcobalt, cobalt-tungsten alloy, and cobalt-molybdenum alloy.

4. The method of claim 2 in which cobalt is the metal from which the gunbarrel is to be made.

5. The method of claim 2 in which an alloy of cobalt-tungsten isemployed as the metal from which the gun barrel is to be made.

6. The method of claim 2 in which an alloy of cobalt-molybdenum isemployed as the metal from which the gun barrel is to be made.

ABNER BRENNER.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 602,212 Desolle Apr. 12, 1898 850,912 Edison Apr. 23, 19071,151,318 Wood Aug. 24, 1915 1,412,174 Eustis et al Apr. 11, 1922FOREIGN PATENTS Number Country Date 12,264 Great Britain of 1888 239,977Great Britain Sept. 24, 1925

2. THE METHOD OF MANUFACTURING A GUN BARREL HAVING A RIFLED BORE OUT OFMETALS THAT ARE HIGHLY RESISTANT TO EROSION AND CORROSION BUT ARE TOOHARD TO MACHINE OR CAST CONVENIENTLY WHICH COMPRISES MAKING A METALLIC"NEGATIVE" FORM WHOSE EXTERNAL DIMENSIONS SUBSTANTIALLY CORRESPOND TOREQUIRED INTERNAL DIMENSIONS FOR THE DESIRED GUN BARREL''S RIFLED BORE,POLISHING SAID "NEGATIVE FORM TO A SMOOTH FINISH, PLATING UPON THE OUTERSURFACE OF SAID "NEGATIVE" FORM A THINN LAYER OF A FUSIBLE METAL WHICHDOES NOT READILY THEREAFTER ELECTROPOLISHING THE FUSIBLE METALCOATED"NEGATIVE" FORM TO A BRIGHT AND SMOOTH FINISH, THEREAFTER ELECTROPLATINGTHE METAL FROM WHICH SAID GUN BARREL IS TO BE MADE TO A DESIRED PART OFTHE DESIRED TOTAL THICKNESS UPON THE OUTER SURFCE OF SAID FUSIBLEMETAL-COATED "NEGATIVE" FORM AT A TEMPERATURE BELOWTHE MELTING POINT OFSAID FUSIBLE METAL COATING, THEREAFTER MACHINING SMOOTH THE OUTERSURFACE OF THE METAL WHICH HAS BEEN THUS ELECTROPLATED UPON THE FUSIBLEMETAL-COATED "NEGATIVE" FORM IN ORDER TO ELIMINATE THE CONTOUR OF THEUNDERLYING LANDS AND GROOVES FROM THE SUBSEQUENT PLATING, THEREAFTERRESUMING ELECTROPLATING THE METAL FROM WHICH SAID GUN METAL IS TO BEMADE AS AFORESAID UNTIL THEDESIRED TOTAL GUN BARREL THICKNESS PLUS AMARGIN FOR FINAL MACHINING HAS BEEN REACHED, THEREAFTER HEATING THE THUSELECTROLATED "NEGATIVE" FORM TO A TEMPERATURE HIGH ENOUGH TO MELT ANDELIMINATE SAID FUSIBLE METAL COATING FROM SAID "NEGATIVE" FORM,THEREAFTER EXTRACTING SAID "NEGATIVE" FORM FROM THE RESULTANT GUN BARRELTHAT HAS BEEN ELECTROFORMED THEREAROUND, AND THEN MACHINING THE OUTSIDEWALL SURFACE OF THE RESULTANT GUN BARREL TO THE DESIRED OVERALLCROSS-SECTIONAL DIMENSIONS.